Dwarves and their underground cities and the vast network of tunnels that connect them, a stereotype older than Tolkien. What I wonder is how would warfare be waged in this tightly restricted area?

Say there are two sides, one which is numerically superior,the rebels, by a wide margin but has little in the way of training, armor, and melee weapons but does have access to muskets and explosives to combat the other side, the nobles, which do have access to trained and capable infantry that are heavily armored and armed but opposed to the use of muskets for their limited use underground and explosives for the risk of damaging tunnels and vital infrastructure. The rebels have an interest in taking over the nation and ousting the nobles by either exile or execution. Now specifically how would warfare be waged with as little damage done to infrastructures such as tunnels, ventilation shafts, and the pipes that carry water and air throughout the nation? This infrastructure is much more expensive to replace than maintain and the rebels wish to keep as much infrastructure intact as possible because of their interest in running the place after the nobles are defeated.

With this in mind, what strategies could each side employ to either quell the rebellion or oust the nobles with as little damage to infrastructure as possible?

EDIT: Time to clarify how the cities actually are designed and what they look like. and maybe one little fact about my dwarves.

There are multiple cities of various size and their size is three dimensional with multiple tiers and levels instead of being based on a flat plane. An answer immediately resonated to me how best to describe the cities and that would be as geofronts are rather hollowed cavities in the earth. The houses are built out towards the outer edge of the geofront in the form of terraces. There are also large cylindrical walls spaced out in front of the outer edges in which more houses are built in a terraced fashion and there are also streets held by stone pillars which also interconnect them. Think of an onion that has many layers and the area in between these layers act as streets. the closer to the center you get, the wealthier the occupants.

Now onto the tunnels that interconnect these cities. If you've ever played Dragon Age you can get a good idea if you imagine the deep roads. However, unlike the deep roads, these tunnels don't have magma flowing their length on either side and they aren't infested with darkspawn. These tunnels are also shorter and slightly wider and the support pillars are placed in the center and in front of each of these pillars are large illuminating crystals encased in glass that act as giant lanterns which solve the problem of lighting. The tunnels act as a sort of highway between the cities. The dwarves also have manually powered vehicles like bicycles which are used in place of horse-drawn carts which would be the main transportation of goods across cities. little fun fact, the dwarves also have bike races across the length between two cities for rewards of gold and recognition from the public to distract them from their very boring lives.

Now how about the air. Air is pumped in from the surface into large pipes that sprawl throughout the nation, delivering air to the dwarves who live underground. Additionally, water is also pumped from aquifers into a different set of pipes which supplies water to the nation. There are also some cities on the surface which cultivate crops which are brought down to the cities in addition to food imported from trade with humans.

The cities on the surface are a fair bit smaller than those below ground and are where the air is pumped in from. These surface cities are built outside of an entrance to one of the subterranean cities and outside of these surface cities are where crops and animals are cultivated.

I hope this gives a much better idea of the dwarven civilization in my world.

$\begingroup$I'll let those who know warfare answer this, but let me suggest you check out Cappadocia. There are entire subterranean citadels there, some dating back to pre-Greek Phrygians. Given the history of Asia Minor, there must have been any number of battles fought in those tunnels, and the defenders surely tried to preserve as much of the infrastructure as possible.$\endgroup$
– TumbislavNov 3 '18 at 17:57

$\begingroup$@AlbertoYagos But how would they control the gas and how would it be deployed? It can't just be pumped into the ventilation because that air is also carried to numerous other locations which may include friendly personal.$\endgroup$
– VaolorNov 3 '18 at 18:37

$\begingroup$Muskets and explosives in caves/tunnels are a definite non-starter. There's a TREMENDOUS (really more than you can imagine) amount of smoke and noise, and no place for it to go.$\endgroup$
– RonJohnNov 3 '18 at 20:40

$\begingroup$See "The Lords of Quarmall", by Fritz Lieber, which can be found in the collection Swords Against Wizardry, available at Amazon. If you like swords & sorcery stories and haven't read Lieber's tales of Fafhrd and the Grey Mouser, you're in for a treat... :-)$\endgroup$
– Bob JarvisNov 3 '18 at 22:56

6 Answers
6

Normally I would vote to close a question asking for "what tactics..." as too broad or primarily opinion-based... but subterranean narrows the question so honking much that I can't justify either condition. Congratulations!

Now, on with the answer...

Let's ignore munitions for a moment. They are so much of a game-changer that they deserve special treatment.

Condition #1: Choke-point warfare

Even if the dwarves have widened caves and tunnels into wide areas, there's only so much widening that's practical and expected. And even then, it's not open warfare. That means no flanking. This makes warfare brutal and personal.

Body removal is a huge problem. It won't take long for bodies to seriously congest pathways. Your warring parties would either have treaties in place governing the necessary removal of bodies, or would resort to ambush-tactics when someone starts to remove the bodies. Of course, bodies decompose, which means you can't just leave them there. The stench in a restricted system like caves would be enormous. Which is very advantageous for whomever is upwind in the cave system. Yuck, but I can actually see a particularly ruthless foe resorting to minor ambush tactics to keep the enemy from clearing the path just to let the stench roll downwind to sicken the armies & residents in those locations.

Even though Tolkein, D&D, and most of the fantasy world tend to depict Dwarves as small, heavily armored tanks, that would be incredibly cumbersome in tight quarters where swinging space-consuming weapons (aka, battle axes) would mean one hopefully-very-tough dude is up front doing 99.9% of the fighting. Now, to be honest, I can see the Dwarves developing a champion system not unlike Japanese bushido where combat would be frequently between (and decided by) just two combatants. But let's assume everybody's really torqued at each other and we need to get more people into the fray. In that case, I'd see a lighter armor fencing-style of combat forming, where damage is caused by quick slashes and thrusts rather than massive two-handed chops or even a dual-light-hammer style (think 4# engineering hammers) where finesse is more important than force-of-impact. If some idiot did come forward wearing thick plate (party pooper), then a simple 4-6 man battering ram would quickly force this dude to the next curve-in-the-cave wall where he would be quickly opened like a can of tuna without the use of a can opener.1

Gas is your friend! Which means having control of the upwind-side of the passage is a really big deal. Simple "I'll control the passage in an hour!" gasses can be made with sulfer and fire or even just green leaves (smoke is a very practical way of clearing a cave). But what would really reduce your enemy's numbers is to use either an asphyxiant gas like natural gas or propane to displace the oxygen in the air or a carbon filter or stuff like this material to remove the oxygen from the air. That'll teach them to stop sending their tribute!

Finally, to build on Henry's answer, torches and concave reflectors or even optics would become powerful for short-distance blind-thy-enemy tactics. It would be easy enough to retreat a few dozen feet to the next cave turning to avoid the powerful light, and it has the limitation of creating massive contrast (think "shadows are really easy to hide in"), but as a support weapon used to momentarily blind the enemy at the beginning of combat it could be very useful.

Condition #2: Urban fighting?

The next question is, how do people actually live in caves? Tolkein liked to portray massive open cities (so to speak), but I doubt that would be the case. Mines are a pain the butt and keeping the roof off the floor is a big part of the problem. Support structures are expensive and require serious planning and engineering.

I suspect that "cities" are more like warrens where "roads" are caves with living quarters carved into the walls along the caves or tunnels. Each home becomes an ambush point, but the basic fighting style wouldn't change. Therefore, no "urban fighting." It's all still choke-point fighting.

However, this means that gas and/or smoke becomes really important to clear out rooms/houses/complexes. Places that might not have a second entrance/exit/access point. You should be thinking "smoke bomb" and "tear gas." Note that the possibility of war may force the construction style to have back doors in many "buildings" (a group of rooms used for a specific purpose, whether a family dwelling, a government office building, or a factory). Those back doors would empty into, perhaps, small tunnels like alleys that would also serve as escape and/or ambush access if the enemy got into the warren city.

Note that as I write this, "upwind control" is becoming a bigger and bigger issue. Just like we on the surface wanting to control the top of a hill or ridge, the army that controls "upwind" controls the battlefield. The ability to shift the direction of windflow would be a huge benefit for an army... and a city. Indeed, you would ideally want the ability to over-pressurize your "city" such that you become "upwind" to all tunnels existing your city. Hmmmm... He who has the biggest surface-to-city air pumps has serious combat control. Which means that a ton of your fighting might not be subterranean as control of those surface-to-city pumps (either the pumps themselves or the surface access points) would be massively strategic. Dang.

Condition #3: Munitions

OK, firearms in tunnels aren't as useful as they might seem. Yes, they'd kill the enemy quickly, filling the tunnel with bodies quickly, and filling it with smoke quickly, which affects both sides alike quickly... frankly, they'd be more of a pain in the tuckus than anything else, especially since their biggest value (range) is of little use in tunnels and caves.

Black powder as a smoke-causing substance is more useful, but only to the upwind people.

What's really useful, though, is explosives.

Collapsing a tunnel, either to block the advance of a foe or to protect your retreat is useful, if somewhat permanent.

Creating a new tunnel quickly to "flank" the enemy... now that's useful.

Diverting water into the path of an enemy... that's very useful. Better still, unlike collapsing the tunnel/cavern, it's temporary. You can collapse access to the waterflow (theoretically) and recover the tunnel (after you've flushed your enemy from it, of course).

So, explosives good. Firearms bad. Black powder OK.

Of course, building on the torch-with-a-concave-reflector idea is flash powder. The ability to create a really bright burst of light that only affects the enemy is very good. Oh, yes... very good! The evil, vile papparazzi (ptui!) might have a use after all.

1We've all had that experience, right? Where all you have is the meat-tenderizing hammer and a butter knife... but you just have to have that stinking can of tuna? Sure you have! I can't be the only one.

$\begingroup$One really doesn't have room to dodge in narrow tunnels. I think that heavy armor would be the way to go. However, any weapons requiring swinging would be hard to use, as you would hit the walls. Because of this, thrusting weapons such as spears would be preferred, as they have good reach, can be pulled back to hit enemies that are closing in, and do not require space to swing. Also, just blocking up tunnels or partially blocking them and then guarding that point with projectile weapons would probably be effective.$\endgroup$
– Richard SmithNov 3 '18 at 23:07

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$\begingroup$@RichardSmith, I agree, there isn't a lot of room in tunnels, and as you said, there isn't space to swing large objects. Thus, fencing or light hammers. In said case, dexterity is still more valuable than protection from impact and heavy armor makes a fencing sword nearly useless. As for the value of projectile weapons, see my point about firearms. The close quarters of caves/tunnels make the reload time of even a bow fatal. IMO. Your point about spears is good, though, especially a short spear (1.5 meters or so).$\endgroup$
– JBHNov 4 '18 at 0:49

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$\begingroup$Great answer but I would change the combat style. Hammers means only the front row can fire, but if everyone has Spears you can use the most perfect phalanx situation in combat. Spears have a small area they deliver the force into allowing it to pierce armor effectively and with thrusts you are unlikely to get in another dwarf's way. Besides tunnels, any open space is likely to have a Curved roof with its highest point in the middle. This allows Javelins to shine as a ranged weapon, and crossbows are perfect for harrowing enemies trying to pass a tunnel. But what about moving walls and such?$\endgroup$
– DemiganNov 4 '18 at 10:50

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$\begingroup$Why is dexterity more important? What does it give you? Armor does not actually restrict movement by much. See youtube.com/watch?v=5hlIUrd7d1Q Also, "heavy" warhammers were never really used. Real 1 handed warhammers looked more like modern tool hammers than the huge fantasy hammers. A tool hammer still needs a lot of space to swing. And you use projectile weapons from behind cover, of course. Block off 3/4ths of the tunnel with rubble, then shoot your enemies behind your cover.$\endgroup$
– Richard SmithNov 4 '18 at 14:00

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$\begingroup$In large scale battles, soldiers mostly poked at each other with polearms while in lines, which meant that there was not much space for dodging. And by the time firearms were prevalent, pretty much everyone had at least munition plate. You say a lightly armored fencer would dance circles around a heavily armored soldier, but dancing impossible in massed battle or in a tunnel. Also, rapiers and such would be terrible against armor. A fencer would have to stab to a joint and penetrate chain + gambeson, while the armored soldier just needs to get a few good hits with his weapon.$\endgroup$
– Richard SmithNov 5 '18 at 2:57

In stories of underground civilization, short shrift is given to ventilation. But ventilation is paramount if you are working or living underground. This is best laid out in the history of mining and working in deep mines. Gases coming up from below can be poisonous, or explosive, or kill by excluding oxygen. Your own efforts can consume the oxygen, especially if you have fires. The illustration shows various methods for getting air exchange down into a mine including bellows, pumps. One could also have a shaft in which there is a fire to produce an up current and a separate shaft to allow ingress of fresh air. Read more - https://web.mst.edu/~tien/218/218-VentHistory.pdf

In any case, fresh air is the life blood of any underground endeavor. There will be connections to the surface for ventilation (as stated in the question) and control of these will be control of the underground empire.

It depends on the size of your nation and its cities

The answers by Wilk and JBH are very detailed and quite accurate under certain assumptions. And that is that your cities are "small" and the entire infrastructure is primarily composed of small tunnels large enough to allow your mining equipment to be transported (or perhaps a little bit larger than that).

Reading your question again made me think that you might be envisioning a network of Geofronts(2) each connected to others via various tunnels that would act as highways between them. These, of course, would be huge feats of engineering that would take years of development and planning but let's assume that the Dwarven Empire can boast of being able to build such grand structures at the height of their power. We can also assume that such meticulous planning also involved solving the issues of ventilation with multiple redundant air shafts and "greenery". (That these shafts would be huge and/or porous and that the greenery would need to thrive in low-light conditions is a separate topic of discussion. There are ways to prevent outside intruders in these cases that are also beyond the scope of the question.)

So, what kind of warfare might be feasible in this kind of environment? Overall, Urban Warfare would dictate most combat conditions in this kind of superstructure. There would be two kinds of battles that each side would have to wage: tunnel battles and city battles. Tunnel battles would involve fighting for control of tunnels, both their entry and relay points ("villages" present between cities) and would most likely resemble JBH's choke-point warfare. This depends a lot on the width of the tunnel. (A "Mega tunnel" would be less of a choke point and more of a front.) Keep in mind that sealing tunnels, bypassing and/or building new tunnels might be commonly employed tactics, especially to avoid the dangerous ventilation and choke point issues. Dwarves are master tunnelers after all!

City warfare would resemble traditional urban warfare. Here, an attacking force would be trying to take control of an entire city and its infrastructure and use that city as a staging point to attack the next city or cities (tunnel warfare again). As wikipedia states:

Fighting in urban areas negates the advantages that one side may have
over the other in armour, heavy artillery, or air support.

There would be no air support here, but heavy artillery (c. 18th century canons) can be employed by either side. This section summarizes the usual conditions encountered in urban warfare:

Tactics are complicated
by a three-dimensional environment, limited fields of view and fire
because of buildings, enhanced concealment and cover for defenders,
below-ground infrastructure, and the ease of placement of booby traps
and snipers.[citation needed]

Another thing to consider is the effect on civilians regardless of alignment:

Some civilians may be difficult to distinguish from combatants such as
armed militias and gangs, and particularly individuals who are simply
trying to protect their homes from attackers.

A caveat: If you only have a single mega city then the scenario is slightly different. Instead of island hopping, you may have urban warfare for those vying for control of the city (rebels), and tunnel warfare for those vying for control of the surrounding mines (nobles). Since the rebels would be commoners and numerically superior, they would already have influence in both the mines and the city slums.

To summarize (TL;DR):

If your cities and nations are "small" and are mainly structured around narrow tunnels then ventilation control and choke point warfare will be an army's main tools.

If your cities are "huge" then more traditional urban warfare methods would be employed coupled with tunnel warfare when "city hopping".

EDIT: Based on the question's recent edits, I don't think my response would change much. The only difference I can spot is that the ventilation shafts/surface cities could now be used as ingress points into the city. Dwarves that usually preferred to use tunnels to cross cities, might find it tactically advantageous to use the surface to reach other cities!

$\begingroup$What all our answers is pointing out is that the OP needs to design his underground habitat before he can ask us how to strategize combat. That almost is enough to close the question.... Well, almost... One hates to put a stop to so many good answers.$\endgroup$
– JBHNov 4 '18 at 1:07

$\begingroup$@JBH Thanks for saying my need to clarify the size of the cities and how the cities are designed. I may edit it into the question.$\endgroup$
– VaolorNov 4 '18 at 1:17

$\begingroup$@JBH I've now added in a fair bit of details that I hope will give a much better idea to the dwarves cities and tunnels.$\endgroup$
– VaolorNov 4 '18 at 2:00

$\begingroup$I've reached my main SO points goal! I'm happy! :D Thanks to everyone who supported my answer :). @JBH You made an excellent point that more information was needed in the question! And yes, it's fun to read the different answers to this fun question! OP: Thanks for adding all that detail in your question! It is very helpful for picturing your scenario.$\endgroup$
– stuxNov 4 '18 at 5:44

Light, or more accurately, the ability to operate in the absence of light is the great strategic advantage that the rebel workers have over the nobles and their trained militia. The militia was trained to handle combat with other nations, out in the daylight, above ground. Meanwhile, the working class, who became the rebels have been living in the caves for their entire lives. They are intimately familiar with their battleground and the intricacies of working in the absence of light.

You can quell the rebellion by showing that you control the air supply. Deploy a gas that is too heavy to go very far (and temporarily block off some key shafts to keep it from spreading), or maybe a powder, and that has no adverse effects beyond making the people who breathe it horribly ill for a few hours (vomiting, diarrhea, etc...). If you want them to remember this every time they use those tunnels, make it fast acting so the place reeks. If you need to use those tunnels later, then make it delayed acting so they get ill at home (as long as they know you caused it).

The rebels might also be able to do this to the nobles but it depends on how concentrated they are. I'm guessing they have larger homes and more space in general. But you could hit an entertainment or shopping venue that only the rich attend. This won't hit them where they live though, like what the nobles can do to the rebels.

Weapons we can actually look at WW1&2 trench and tunnel warfare for ideas not to mention the countless other times tunnel fighting has popped up in history.

Counterintuitively for dwarves axes make for really poor choices for underground combat, basically anything you have to swing is bad since you often won't have the space. Short swords, short spears and other compact stabbing weapons are good choices, their motions are compact and direct. Likewise small shields are better than large ones. Basically any weapon you could not use in a closet is a poor choice.

Crossbows are just about the only ranged weapon that works since they also do not need much room. Guns can share this feature but you need to keep them short, long muskets become unwieldy and impossible to load. Shortguns like pistols and blunderbuss are usable however. Note however that ranged combat is limited, usually you will only get one shot unless you have long corridors. Builder might design these at defensive choke points to make it as hard as possible for attackers. Some old fortresses were designed with saw tooth or right angle expansion walls so defenders had cover and attackers did not.